Análise do cimento álcali ativado quando sujeito à reação álcali-agregado

Abstract

The growing environmental concern has stimulated studies for the development of alternative cements, with reduced greenhouse gas emissions in its manufacture. One of these is the alkali activated cement (CAT), which in addition to providing a reduction in carbon emissions, also allows the reuse of industrial waste, such as blast furnace slags. Some studies have already reported good results in terms of mechanical strength and durability of this cement, but there are still few studies that evaluate its performance when exposed to the alkali-aggregate reaction (AAR). This reaction is a pathological manifestation that affects mainly dams and other constructions exposed to humid environments, where the cement alkalis combine with reactive minerals of the aggregate, creating an expansive product capable of generating cracks and compromise concrete structures. One of the factors that influences the development of the RAA for Portland cement is the amount of alkalis available in its composition. As alkali activated cements generally present a greater amount of alkalis than the Portland, the need to further analyze the behavior of CAT's when subjected to this reaction comes up. In this study, the performance of blast furnace slags activated with contents of 4 and 5% of NaOH is evaluated when in contact with reactive aggregate of the region of Pato Branco-PR. There were carried out essays of expansion in mortar and concrete, mechanical strength, visual and microstructural analysis. As a comparison, the same tests were performed on two types of Portland cement (CPV-ARI and CPIV-RS). From the results, there was found a good behavior of the alkali activated cement to the RAA, with lower expansions that established by standards, and no strength or structural integrity losses. The alkali activator content had a little influence on the behavior of the CATs, where the minor amount of NaOH, which results in smaller alkali equivalent, proved more resistant to the reaction. Even for the higher level of activator, results were good and comparable to the CPIV-RS, Portland cement recommended for inhibiting alkali-aggregate reaction.